Fuel rail assembly including fuel separation membrane

ABSTRACT

As one example, a fuel rail assembly for supplying pressurized fuel to a plurality of cylinders of an engine is provided. The fuel rail assembly includes a fuel rail housing defining an internal fuel rail volume having at least a first region and a second region; a fuel separation membrane element disposed within the fuel rail housing that segregates the first region from the second region. The membrane element can be configured to pass a first component of a fuel mixture such as an alcohol through the membrane element from the first region to the second region at a higher rate than a second component of the fuel mixture such as a hydrocarbon. The separated alcohol and hydrocarbon components can be provided to the engine in varying relative amounts based on operating conditions.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.11/962,683, “Fuel Rail Assembly including Fuel Separation Membrane,”filed on Dec. 21, 2007, now U.S. Pat. No. 8,550,058, the entire contentsof which are hereby incorporated by reference for all purposes.

BACKGROUND AND SUMMARY

Internal combustion engines utilizing two or more different fuels havebeen proposed. As one example, the papers titled “Calculations of KnockSuppression in Highly Turbocharged Gasoline/Ethanol Engines Using DirectEthanol Injection” and “Direct Injection Ethanol Boosted GasolineEngine: Biofuel Leveraging for Cost Effective Reduction of OilDependence and CO2 Emissions” by Heywood et al. describe engines thatare capable of using multiple fuels. Specifically, the Heywood et al.papers describe directly injecting ethanol into the engine cylinders toimprove charge cooling effects, while relying on port injected gasolineto providing a majority of the combusted fuel over a drive cycle. Theethanol, in this example, can provide increased octane and increasedcharge cooling due to its higher heat of vaporization in comparison togasoline, thereby reducing knock limits on boosting and/or compressionratio. This approach purports to improve fuel economy and increaseutilization of renewable fuels.

The inventors of the present disclosure have recognized that requiring auser to re-fuel the engine system with two or more separate fuels (e.g.,gasoline and ethanol), in order to achieve the advantages described byHeywood et al., can be burdensome. As one approach, United Statesprinted publication number 2006/0191727 by Usami et al. describes anelectric power generation system that includes a fuel storage unithaving an ethanol permeable membrane for separating the ethanol from amixed fuel including ethanol and gasoline. This publication describeshow ethanol separation can be performed in proportion to the pressuredifference across the permeable membrane and also according to thetemperature difference across the membrane.

However, the inventors herein have recognized a variety of issuesassociated with the approach taken by Usami et al. As one example, theinventors have recognized that engine packaging constraints on-board avehicle may preclude the addition of a fuel separator or may reduce theeffective size of the separator. A reduction in the separator size canreduce fuel separation rates, which may in turn impair engineperformance where the fuel to be separated is temporarily unavailable oravailable in a reduced amount due to the reduced separation rate. Asanother example, the use of a dedicated heater as taught by Usami et al.to improve the separation rate by way of heat addition is also limitedby the similar packaging constraints.

To address these and other issues, the inventors herein have provided afuel rail assembly for supplying pressurized fuel to a plurality ofcylinders of an engine. As one example, the fuel rail assembly comprisesa fuel rail housing defining an internal fuel rail volume having atleast a first region and a second region; a fuel separation membraneelement disposed within the fuel rail housing and segregating the firstregion from the second region, said membrane element configured to passa first component of a fuel mixture through the membrane element fromthe first region to the second region at a higher rate than a secondcomponent of the fuel mixture; a fuel inlet disposed on the fuel railhousing, said fuel inlet configured to admit the fuel mixture to thefirst region; a plurality of fuel outlets disposed on the fuel railhousing, wherein each of said fuel outlets are configured to supply atleast a portion of the fuel mixture from the first region to arespective one of said plurality of engine cylinders; and at least onemembrane outlet disposed on the fuel rail housing and configured tosupply at least a portion of the first component that has passed throughthe membrane element from the second region to a location external thefuel rail housing.

By placing the fuel separation membrane within the fuel rail assembly,which is in relative close proximity to the engine, the fuel separationmembrane and the fuel mixture to be separated by the membrane can be atleast partially heated by the engine. In this way, the fuel separationrate can be increased without requiring a separate heater, therebyreducing cost and other associated packaging constraints. Further, inthis way, it is possible to utilize a fuel pump to pressurize fuel forinjection to the engine, as well as for improved separation of the fuelmixture.

The inventors herein have also recognized that the fuel separation ratecan be further increased by increasing the surface area of the fuelseparation membrane relative to the volume of the separator. As oneexample, the surface area of the membrane may be increased for a givenseparator volume by supporting the membrane on a substrate that forms anon-planar membrane element within the fuel rail, such as a tube. Bysupplying the pressurized fuel to the external surface of the tubularmembrane element, the substrate can be loaded in compression, which canprovide an additional strength advantage for some substrate materialssuch as ceramics or other materials that are relatively stronger whenloaded in compression than tension.

The inventors herein have also recognized that a plurality of separatemembrane elements within a common fuel rail assembly can furtherincrease the separation rate for a given separator volume. For example,by utilizing multiple smaller tubes for the membrane elements, the ringstress in the substrate can be reduced, thereby enabling a furtherreduction in wall thickness of the substrate. A reduction in wallthickness and increased surface area of the membrane elements canfurther increase the fuel separation rate while also reducing packagingconstraints. These and other advantages will be appreciated in light ofthe following specification and accompanying drawings.

In still another embodiment, a method of operating a fuel system for aninternal combustion engine may be used, comprising: supplying apressurized fuel mixture to a fuel rail, said fuel mixture including ahydrocarbon component and an alcohol component; separating at least aportion of the alcohol component from the fuel mixture by passing atleast said portion of the alcohol component through a fuel separationmembrane element disposed within the fuel rail to obtain an alcoholreduced fuel mixture; delivering the alcohol reduced fuel mixture fromthe fuel rail to at least a plurality of cylinders of the engine viainjectors fluidly coupled with the first fuel rail; and supplying theseparated alcohol component to the engine. In this way, it is possibleto utilize a fuel pump to pressurize fuel for injection to the engine,as well as for improved separation of the fuel mixture.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic depiction of an example fuel system for anengine.

FIG. 2 shows a schematic depiction of an example air intake and exhaustsystem for an engine.

FIG. 3 shows a schematic depiction of an example cylinder of an internalcombustion engine.

FIG. 4 shows a schematic depiction of an example fuel separationprocess.

FIG. 5 shows a schematic depiction of a first example of a fuel railassembly including a fuel separation membrane element.

FIG. 6 shows a schematic depiction of a second example of a fuel railassembly including a plurality of fuel membrane elements.

FIGS. 7A-7F show example cross-sections of the fuel rail assemblies ofFIGS. 5 and 6.

FIG. 8 shows a flow chart depicting an example fuel delivery controlstrategy.

FIG. 9 shows a flow chart depicting an example fuel separation controlstrategy.

FIG. 10 shows a control map depicting how fuel delivery can be varied inresponse to operating conditions.

DETAILED DESCRIPTION

FIG. 1 shows a schematic depiction of an example fuel system 100 for afuel burning engine 110. As one non-limiting example, engine 110 can beconfigured as an internal combustion engine that is configured on-boarda vehicle as part of a propulsion system. However, engine 110 caninclude other engine types and can be configured in other suitableapplications. In this particular example, engine 110 includes fourcombustion chambers or cylinders indicated at 112, 114, 116, and 118. Inother examples, engine 110 may include any suitable number of cylinders.Engine 110 will be described in greater detail with reference to FIGS. 2and 3.

In this example, each cylinder of engine 110 can receive at least twoseparate fuels having different compositions in varying relative amountsbased on operating conditions. Thus, each engine cylinder can receive afirst fuel as indicated at 170 via a first fuel rail assembly 130 andcan receive a second fuel indicated at 180 via a second fuel rail 160.As one example, the first fuel provided to the engine at 170 can includea higher concentration of at least one component than the second fuelprovided to the engine at 180. Similarly, the second fuel can include ahigher concentration of at least one other component than the firstfuel. For example, the first fuel provided to the engine via fuel railassembly 130 can include a higher concentration of a hydrocarboncomponent (e.g. gasoline, diesel, etc.) than the second fuel provided tothe engine via fuel rail 160, while the second fuel can include a higherconcentration of an alcohol component (e.g. ethanol, methanol, etc.)than the first fuel. As will be described in greater detail withreference to FIGS. 8 and 10, the relative amounts of these two fuelsthat are delivered to the engine can be varied by control system 190 inresponse to operating conditions.

These first and second fuels can be separated from a fuel mixture 121on-board the vehicle before being delivered to the engine. Fuel mixture121 can be provided to a fuel tank 120 during a refueling operationindicated at 102 via fuel passage 104. The fuel mixture can include anysuitable mixture of hydrocarbon and alcohol components. For example, thefuel mixture may include E10 (a mixture of approximately 10% ethanol and90% gasoline by volume), E85 (a mixture of approximately 85% ethanol and15% gasoline by volume), M10 (a mixture of approximately 10% methanoland 90% gasoline by volume), M85 (a mixture of approximately 85%methanol and 15% gasoline volume), a mixture including gasoline,methanol and ethanol, or other mixtures of alcohol and gasoline.Furthermore, with regard to the above examples, diesel may replacegasoline, or the fuel mixture may include two or more hydrocarbon fuelsand an alcohol. Further still, in some examples, the fuel mixture mayinclude water in addition to an alcohol and/or a hydrocarbon. Controlsystem 190 can receive an indication of the composition of fuel mixture121 via fuel sensor 123, including alcohol concentration, hydrocarbonconcentration, etc. Control system 190 can also receive an indication ofthe amount of the fuel mixture contained within storage tank 120 viasensor 125.

The fuel mixture can be provided to fuel rail assembly 130 from fueltank 120 via fuel passage 124. Fuel passage 124 may include one or moreintermediate fuel pumps. In this particular example, fuel passage 124includes a lower pressure pump 122 and a higher pressure pump 126.During operation of engine 110, control system 190 can adjust operationof pump 122 and/or pump 126 to provide the fuel mixture to fuel railassembly 130 at any suitable pressure and/or flow rate in response tofeedback received from pressure sensor 136. As one example, the pressureof the fuel mixture supplied to the fuel rail assembly 130 may beadjustable between a pressure of 4 bar and 200 bar. However, otherinjection pressures may be used. In some examples, low pressure fuelpump 122 can be powered by an electric motor, whereby control system 190can adjust the level of pump work provided by pump 122 by varying theamount of electrical power that is provided to the pump motor from anenergy source stored on-board the vehicle (not shown). In some examples,high pressure fuel pump 126 can be powered directly by a mechanicaloutput of engine 110 as indicated at 108, such as via a crankshaft orcamshaft of the engine. Control system 190 can adjust the pump workprovided by pump 126 by varying the effective volume of each pumpstroke. While separate pumps 122 and 126 have been presented in FIG. 1,in other examples, a single pump can be used to provide the fuel mixtureto fuel rail assembly 130. As described in further detail herein, one ormore of the fuel pumps may be adjusted to vary a pressure of fueldelivered to the engine, as well as separation pressure, based on anexhaust gas oxygen amount, altitude, and/or humidity. In this way, therate of separation, for example, may be adjusted responsive to operatingconditions.

In this example, fuel rail assembly 130 includes a fuel rail housing 132that defines a first fuel mixture receiving region 133, where the fuelmixture is initially received from fuel passage 124. Fuel rail assembly130 can also include a fuel separation membrane element 134 furtherdefining a second region 135 separate from region 133. Membrane element134 can include a selectively permeable membrane element that permits atleast one component of the fuel mixture to pass through the membraneelement from region 133 to region 135 at a greater rate than at leastone other component of the fuel mixture.

As one non-limiting example, the membrane element can be configured topermit at least an alcohol component of the fuel mixture to permeatethrough the membrane element from region 133 to region 135. However, insome examples, the membrane element may also permit a hydrocarboncomponent of the fuel mixture to permeate the membrane element at asubstantially lower rate than the alcohol component. The term permeantmay be used herein to describe the fuel component or components thatpermeate the membrane element into region 135. In this way, membraneelement 134 can provide a fuel separation function, whereby the permeantcan include a higher concentration of the alcohol component and a lowerconcentration of the hydrocarbon component than the initial fuel mixturedue in part to the selectivity of the membrane element.

In some examples, permeation of the permeant can utilize a process thatmay be referred to as pervaporation. Pervaporation can include acombination of membrane element permeation and evaporation of thepermeant from the membrane element interface with region 135. Referringalso to FIG. 4, a first component 420 (e.g. an alcohol component) canpass through membrane element 134 by sorption at a first membraneelement interface with region 133 followed by diffusion of the componentacross the membrane element, and finally desorption of the componentinto a vapor phase at a second membrane element interface with region135. Thus, the fuel mixture including components 420 and 430 can bereceived at region 133 in a liquid phase (e.g. fuel mixture 121) andcomponent 420 (e.g. an alcohol such as ethanol or methanol) can passthrough membrane element 134 where it can be initially received atregion 135 in a vapor phase. Component 430 (e.g. the hydrocarboncomponent) can be retained within region 133 by the membrane element.However, it should be appreciated that some membrane elements may permitat least some hydrocarbon components to permeate the membrane elementmaterial into region 135, while still providing fuel separationfunctionality.

FIG. 4 further illustrates how membrane element 134 can include aselectively permeable membrane coating 440 forming a layer that issupported on a membrane substrate 450. Substrate 450 can form a supportstructure that enables the membrane element to withstand compressiveforce from the pressurized fuel mixture applied to external membranecoating 440 as indicated at 133. In some examples, membrane coating 440can be relatively more flexible than substrate 450.

Membrane coating 440 may include a polymer and/or other suitablematerial that permits the alcohol component to permeate through themembrane coating at a higher rate than the hydrocarbon component. Forexample, membrane coating 440 may include polyethersulfone that containsboth polar and nonpolar characteristics, with the polar interactiondominant to the outer layer of the membrane coating (e.g. the interfacebetween membrane element 134 and region 133), which permits alcohol topermeate the membrane coating to a greater extent than the hydrocarbons.Additionally or alternatively, membrane coating 440 may include ananofiltration material that utilizes molecule size exclusion and/orchemical selectivity to separate the alcohol component from thehydrocarbon component of the fuel mixture.

Substrate 450 can form a rigid porous tube that defines region 135 forreceiving the permeant. As one non-limiting example, substrate 450 cancomprise zirconia ceramic material or other suitable material havingpores 460 that permit at least an alcohol component of the fuel mixtureto pass from region 133 to region 135. A ceramic material may beselected for the substrate since it has the property of being relativelystrong in compression, and is relatively heat resistant. By supplyingthe higher pressure fuel mixture to the exterior of the membrane elementincluding the membrane coating and a ceramic substrate, the ceramicsubstrate is advantageously loaded and can support the more flexiblemembrane coating.

The rate of transport of a particular fuel mixture component across themembrane element can be dependent on a variety of factors, including thepressure gradient across the membrane element (e.g. pressure differencebetween regions 133 and 135), a temperature of the membrane coating andfuel mixture, and a concentration gradient of the permeant componentacross the membrane element (e.g. between regions 133 and 135). Byincreasing the pressure gradient across the membrane element, thetemperature of the fuel rail assembly, and/or the concentration gradientacross the membrane element, the separation rate of the fuel mixture canbe increased. Conversely, by reducing the pressure gradient across themembrane element, the temperature of the fuel rail assembly, and/or theconcentration gradient across the membrane element, the separation rateof the fuel mixture can be reduced.

Thus, in some example, the control system can vary the pressure gradientacross the membrane element in order to adjust the separation rate ofthe permeant (e.g. the alcohol component) from the fuel mixture. Forexample, the control system can increase or decrease the fuel mixturepressure supplied to region 133 of fuel rail assembly 130 byrespectively increasing or decreasing the pump work provided by pumps122 and/or 126. Additionally or alternatively, the control system candecrease or increase the pressure within region 135 of the fuel railassembly by respectively increasing or decreasing the amount of pumpwork provided by vapor compressor 142. In some examples, vaporcompressor 142 may apply a partial vacuum to region 135 to maintain thepermeant in a vapor phase until it is condensed by condensation system140. Adjustment to the operation of vapor compressor 142 can also adjustthe removal rate of the permeant from region 135, which in turn affectsthe concentration gradient across the membrane element.

The placement of the fuel separation membrane element within the fuelrail provides several advantages. First, the increase in the fuelmixture pressure provided to fuel rail assembly 130 via pumps 122 and/or126 can be used to advantage to promote permeation of the alcoholcomponent of the fuel mixture through the membrane element. In this way,a separate fuel pump is not required for the fuel separation operationand the fuel injection system. Second, the fuel rail assembly can bepositioned at a suitable orientation and/or proximity to the engine toreceive heat generated during the combustion process. The temperature ofthe fuel rail assembly near the cylinder head can be substantiallyhigher than ambient air temperature, for example, the temperature nearthe cylinder head can be approximately 400K. In this way, a separatefuel heater is not required for promoting separation of the alcohol andhydrocarbon components of the fuel mixture. Third, fuel rail assembly130 including the fuel separation membrane element can provide a morecompact fuel separation system from an engine packaging standpoint.

Due to the pervaporation process, the permeant can evaporate from themembrane element interface with region 135 to form a vapor. Acondensation system 140 fluidly coupled with region 135 via vaporpassage 138 can be provided to assist with the removal of the permeantvapor from region 135 of the fuel rail assembly and can condense thepermeant vapor into a liquid phase for subsequent delivery to the enginevia fuel rail 160. Note that in an alternative embodiment, the permeantvapor may be delivered to the engine intake manifold in vapor form to beingested by the cylinders for combustion. Further manifold vacuum may beapplied to further improve the separation and delivery to the cylinderof the vapor.

In one example, condensation system 140 includes vapor compressor 142and a heat exchanger 146. Vapor compressor 142 can be powered by amechanical input from the engine via the crankshaft or camshaft asindicated at 143. Alternatively, vapor compressor 142 can be powered byan electric motor from an on-board power supply such as a battery oralternator. Heat exchanger 146 can be operated to extract heat from thepermeate vapor enabling it to condense to a liquid phase, where it maybe collected at a permeant storage tank 150 as indicated at 151. Heatexchanger 146 can be configured to utilize any suitable working fluidfor removing heat from the permeant, including ambient air, enginecoolant, or other suitable coolant. In some examples, the amount of heatextracted from the permeant can be adjusted by the control system byincreasing or decreasing the temperature and/or flow rate of the workingfluid. The heat exchanger 146 and/or compressor 142 may be adjusted, forexample, responsive to the amount of separation, concentration ofalcohol before and/or after separation, engine operation, exhaustair-fuel ratio, exhaust oxygen content, etc.

In some examples, vapor passage 138 may include a valve that can beopened and closed by the control system to vary the rate at which thepermeant is removed from region 135. As one example, the control systemmay close the valve to reduce the rate of fuel separation as well asreducing the condensation of the permeant at storage tank 150. In thisway, the control system can regulate the amount of permeant that isavailable to the engine via fuel rail 160.

Permeant tank 150 can include a fuel sensor 153 for providing anindication of the composition of the condensed permeant fuel 151. Forexample, sensor 153 can provide an indication of the alcoholconcentration of fuel 151 to control system 190. Permeant tank 150 canalso include a fuel level sensor 155 for providing an indication of theamount of fuel 151 contained within the permeant tank. In some examples,control system 190 can adjust the separation rate at fuel rail assembly130 in response to an amount and/or concentration of fuel 151 storedwithin tank 150. For example, the control system can increase theseparation rate of the permeant if the amount of the permeant fuelstored within tank 150 is below a threshold. Conversely, the controlsystem can reduce the separation rate or discontinue separation of thepermeant if the amount of fuel stored in tank 150 is greater than athreshold. Furthermore, the control system can also increase or decreasethe condensation rate provided by condensation system 140 in response tothe rate of separation.

Permeant 151 can be supplied to fuel rail 160 via one or more fuel pumpsby way of fuel passage 156. For example, a lower pressure pump 157 canbe powered by an electric motor, while a higher pressure fuel pump 158can be powered directly by a mechanical output of engine 110 asindicated at 108. However, in some examples, fuel passage 156 mayinclude only one fuel pump.

FIG. 1 further illustrates how fuel tanks 120 and 150 can includerespective vapor passages 127 and 152 for purging fuel vapors thatdevelop in the ullage space of these tanks Vapor passages 127 and 152can communicate with an air intake passage of the engine via a valve154, as shown in greater detail by FIG. 3. The control system can adjustthe position of valve 154 to increase or decrease the flow rate of fuelvapors to the engine. In some examples, vapor passages 127 and 152 cancommunicate with the air intake passage of the engine via separatevalves.

While FIG. 1 shows a configuration where the fuel mixture entering thefuel rail assembly is not returned to fuel tank 120, in other examples,the alcohol reduced fuel retained by the membrane element can bereturned to the fuel tank. For example, where the alcohol separation viathe membrane element is relatively rapid relative to the rate ofinjection of the alcohol reduced fuel, at least a portion of the alcoholreduced fuel can be circulated back to fuel tank 120 via a recirculationpassage (not shown).

Referring now to FIG. 2, a schematic depiction of an example air intakeand exhaust system for engine 110 is shown. Intake air can be providedto engine 110 via an air intake manifold 210 and products of combustioncan be exhausted from the engine via exhaust manifold 220. Intake aircan be provided to intake manifold 210 via intake throttle 212 andexhaust gases that are provided to exhaust manifold 220 can be treatedby an exhaust catalyst 222. A boosting device such as turbocharger 230can be provided, which includes a compressor 232 configured to provideboosted intake air to intake manifold 210, and an exhaust gas turbine234 configured to extract exhaust energy from the exhaust gases flowingfrom engine 110. Turbine 234 can be rotationally coupled with compressor232 via a shaft 236. Note that in other examples, compressor 232 can beinstead driven by engine 110 or by an electric motor while turbine 234can be omitted. A compressor bypass valve 214 can be provided to enableintake air to bypass the compressor under select operating conditions.Similarly, a turbine bypass valve 224 can be provided to enable exhaustgases to bypass the turbine under select operating conditions. Controlsystem 190 can adjust the position of valves 214 and 224 to respectivelybypass compressor 232 and turbine 234.

FIG. 3 shows a schematic depiction of an example cylinder of internalcombustion engine 110, as well as the intake and exhaust paths connectedto the cylinder. In the embodiment shown in FIG. 3, the example cylinderor combustion chamber 330 can receive two different fuels via twodifferent injectors 366 and 367. Cylinder 330 can be any of cylinders112, 114, 116, and 118 previously described in FIG. 1.

As one example, injector 366 can provide a first fuel to the cylinder asindicated at 170 in FIG. 1, while injector 367 can provide a second fuelto the cylinder as indicated at 180 in FIG. 1. Thus, fuel injector 366can be fluidly coupled with region 133 of fuel rail assembly 130 andfuel injector 367 can be fluidly coupled with fuel rail 160. Thus, asone non-limiting example, injector 367 can provide the permeant fuel tothe cylinder, including a greater concentration of alcohol than theinitial fuel mixture, and injector 366 can provide the portion of thefuel mixture that was retained within region 133 of the fuel railassembly by the membrane element. Therefore, injector 366 can provide afuel having a greater concentration of hydrocarbons and a lowerconcentration of alcohol than the fuel provided by injector 367.

By adjusting the relative amounts of the two different fuels provided byinjectors 366 and 367, it is possible to take advantage of the increasedcharge cooling properties provided by the alcohol component of thepermeant fuel to thereby reduce the tendency of knock. This phenomenon,combined with increased compression ratio, boosting and/or enginedownsizing, can then be used to obtain large fuel economy benefits (byreducing the knock limitations on the engine) and/or large increases inengine performance. As will be described in greater detail withreference to FIGS. 8 and 10, the amount of the alcohol rich permeantfuel provided to the engine can be increased in order to reduce engineknock.

While FIG. 3 shows an example where both of fuel injectors 366 and 367are configured as in-cylinder direct injectors for each cylinder of theengine, in other examples, at least one of injectors 366 and 367 may beconfigured as a port injector and the other as a direct injector. Forexample, injector 366 may be arranged in an air intake passage of theengine and injector 367 may be arranged as an in-cylinder injector.

Cylinder 330 of engine 110 is defined at least partially by combustionchamber walls 332 and further by piston 336 positioned therein. Piston336 can be connected to crankshaft 340. A starter motor (not shown) maybe coupled to crankshaft 340 via a flywheel (not shown), oralternatively direct engine starting may be used. In one particularexample, piston 336 may include a recess or bowl (not shown) to help informing stratified charges of air and fuel, if desired. However, in analternative embodiment, a flat piston may be used.

Cylinder, 330 is shown communicating with intake manifold 210 andexhaust manifold 220 via respective intake valve 352 and exhaust valve354. Note that each cylinder of engine 110 can include two or moreintake valves and/or two or more exhaust valves. Cylinder 330 can have acompression ratio, which may be defined as the ratio of volumes whenpiston 336 is at bottom center to when piston 336 is at top center. Inone example, the compression ratio may be approximately 9:1. However, insome examples where different fuels are used, the compression ratio maybe increased. For example, it may be between 10:1 and 11:1 or 11:1 and12:1, or greater.

Fuel injector 366 is shown directly coupled to combustion chamber 330for delivering injected fuel directly therein in proportion to the pulsewidth of signal FPW received from control system 190 via electronicdriver 368. While FIG. 3 shows injector 366 as a side injector, it mayalso be located overhead of the piston, such as near the position ofspark plug 398. Alternatively, the injector may be located overhead andnear the intake valve to improve mixing. Fuel may also be delivered tocylinder 330 via fuel injector 367. Fuel injector 367 is shown directlycoupled to combustion chamber 330 for delivering injected fuel directlytherein in proportion to the pulse width of signal FPW received fromcontrol system 190 via electronic driver 369. While FIG. 3 showsinjector 367 as a side injector, it may also be located overhead of thepiston, such as near the position of spark plug 398. Alternatively, theinjector may be located overhead and near the intake valve to improvemixing. Such a position may improve mixing and combustion due to thelower volatility of some alcohol based fuels.

Intake manifold 210 is shown communicating with throttle body 342 viathrottle plate 212. In this particular example, throttle plate 212 ismoveably coupled to electric motor 362 so that the position ofelliptical throttle plate 212 can be controlled by control system 190via electric motor 362. This configuration may be referred to aselectronic throttle control (ETC), which can also be utilized, forexample, during idle speed control. In an alternative embodiment (notshown), a bypass air passageway can be arranged in parallel withthrottle plate 212 to control inducted airflow during idle speed controlvia an idle control by-pass valve positioned within the air passageway.

Exhaust gas sensor 326 is shown coupled to exhaust manifold 220 upstreamof catalytic converter 222. Sensor 326 may be any suitable sensor forproviding an indication of exhaust gas air/fuel ratio, including alinear oxygen sensor, a UEGO, a two-state oxygen sensor, an EGO, a HEGO,or an HC or CO sensor. In this particular example, sensor 326 is atwo-state oxygen sensor that provides signal EGO to control system 190which converts signal EGO into two-state signal EGOS. A high voltagestate of signal EGOS indicates exhaust gases are rich of stoichiometryand a low voltage state of signal EGOS indicates exhaust gases are leanof stoichiometry. Signal EGOS may be used to advantage during feedbackair/fuel control to maintain average air/fuel at stoichiometry during astoichiometric homogeneous mode of operation. Additionally, sensor 326can provide feedback to the control system to enable a prescribed ratioof the first and second fuels to be delivered to the engine.

Distributorless ignition system 388 can provide an ignition spark tocombustion chamber 330 via spark plug 398 in response to spark advancesignal SA from control system 190. Control system 190 may causecombustion chamber 330 to operate in a variety of combustion modes,including a homogeneous air/fuel mode and a stratified air/fuel mode bycontrolling injection timing, injection amounts, spray patterns, etc.Control system 190 can independently control the amount of fueldelivered to the cylinder by fuel injectors 366 and 367 so that thehomogeneous, stratified, or combined homogenous/stratified air/fuelmixture in chamber 330 can be selected to be at stoichiometry, a valuerich of stoichiometry, or a value lean of stoichiometry.

As previously described with reference to FIG. 1, internal combustionengine 110, including a plurality of combustion chambers, can becontrolled by a control system 190. As one example, control system 190can be configured as an electronic engine controller and may include amicrocomputer, including microprocessor unit 302, input/output ports304, an electronic storage medium for executable programs andcalibration values shown as read only memory (ROM) chip 306 in thisparticular example, random access memory (RAM) 308, keep alive memory(KAM) 310, communicating via a data bus. Control system 190 is shownreceiving various signals from sensors coupled to engine 110, inaddition to those signals previously discussed, including measurement ofinducted mass air flow (MAF) from mass air flow sensor 320 coupled tothrottle body 342; engine coolant temperature (ECT) from temperaturesensor 313 coupled to cooling sleeve 314; a profile ignition pickupsignal (PIP) from Hall effect sensor 318 coupled to crankshaft 340; andthrottle position TP from throttle position sensor 321; absoluteManifold Pressure Signal MAP from sensor 322; an indication of engineknock from knock sensor 396; and an indication of requested enginetorque from vehicle operator 392 by pedal 390 via pedal position sensor394. These and other sensors can provide an indication of operatingconditions to the control system. Engine speed signal RPM can begenerated by control system 190 from signal PIP in a conventional mannerand manifold pressure signal MAP from a manifold pressure sensorprovides an indication of vacuum, or pressure, in the intake manifold.During stoichiometric operation, this sensor can give an indication ofengine load. Further, this sensor, along with engine speed, can providean estimate of charge (including air) inducted into the cylinder. In oneexample, sensor 318, which is also used as an engine speed sensor,produces a predetermined number of equally spaced pulses everyrevolution of the crankshaft.

Continuing with FIG. 3, a variable camshaft timing system is shown forcontrolling the operation of valves 352 and 354. For example, cam shaft351 can control the opening and closing timing of intake valve 352. Acam timing sensor 355 can provide an indication of intake valve timingto control system 190. A cam shaft 353 can control the opening andclosing timing of exhaust valve 354. A cam timing sensor 357 can providean indication of exhaust valve timing to control 190. In some examples,valve timing can be adjusted by a variable cam timing system that canvary the rotational relationship between the cam shafts and thecrankshaft of the engine. In this way, the intake and/or exhaust valvetimings can be adjusted relative to the position of the piston.Furthermore in some examples, cam profile switching may be used toenable the control system to vary the timing and/or lift of the valves.Further still, in alternative embodiments, valves 352 and/or 354 may becontrolled by electromagnetic valve actuators.

Referring now to FIG. 5, a non-limiting example of fuel rail assembly500 is shown. Fuel rail assembly 500 can represent fuel rail assembly130 previously described with reference to FIG. 1. Fuel rail assembly500 can include a fuel rail housing 510 that defines a fuel mixturereceiving region 570 for receiving the fuel mixture. Region 570 of 500can represent region 133 of fuel rail assembly 130. In this example,fuel rail housing 510 includes fuel rail wall 508 and end caps 550 and560. However, in other examples, end caps 550 and 560 can be formedintegrally with the fuel rail wall. End caps 550 and 560 can serve asboth sealing plugs for the ends of the fuel rail assembly as well assupporting the ends of the membrane element and internal membraneelement support structure.

Fuel rail housing 510 further includes a fuel inlet port 520, which canbe used to supply a fuel mixture to region 570 as indicated by arrow542. Fuel rail housing 510 can further include one or more outlet ports,one of which is shown at 530. In this particular example, outlet port530 can be fluidly coupled with a fuel injector, a fuel receiving end ofwhich is shown at 532. Fuel injector 532 can deliver fuel to at leastone cylinder of the engine. For example, injector 532 can representinjector 366 shown in FIG. 3. In other examples, the fuel outlet portmay provide fuel to two or more cylinders of the engine. For example, aplurality of injectors may receive fuel from a single outlet of the railso that substantially equal fuel composition may be delivered to theinjectors.

Fuel injector 532 can be configured as a port injector or alternativelyas a direct injector, as shown in FIG. 3, for example. While only asingle outlet port is shown in this example, it should be appreciatedthat fuel rail assembly 130 can include two or more fuel outlet portsthat may be each fluidly coupled with a fuel injector. For example, asshown in FIG. 1, fuel rail assembly 130 can include at least four fueloutlet ports that each service separate engine cylinders via theirrespective fuel injectors. Thus, in some examples, the fuel railassembly may include the same number of fuel outlet ports as enginecylinders. However, where the engine includes two fuel rail assemblies130 for servicing separate banks of engine cylinders (e.g. for a twinbank V-8 engine), each fuel rail assembly may include a number of fueloutlet ports equivalent to the number of cylinders that are serviced bythe fuel rail assembly.

Fuel separation membrane element 582 shown in FIG. 5 can representmembrane element 134 that was previously described with reference toFIGS. 1 and 4. In this particular example, region 572 is partiallydefined by membrane element 582 and is further defined by end caps 550and 552. End cap 550 further includes an opening or port for permittingthe permeant to be removed from region 572 of the fuel rail assembly.For example, as shown in FIG. 1, the permeant can be removed from region135 via vapor passage 138 and as shown in FIG. 1, fuel may be suppliedto fuel inlet port 520 via fuel passage 124.

In some examples, membrane element 582 may be supported or held inposition within housing 510 by one or more supports located atprescribed intervals along the longitudinal length of the membraneelement as indicated generally at 598. The supports illustrated externalto the membrane element at 598 are in contrast to substrate 450 that wasdescribed with reference to FIG. 4. However, in some examples, support598 can be integrally formed with the substrate of the membrane element.An example cross section of support 598 is shown in FIG. 7.

FIG. 6 shows a fuel rail assembly 600 as an alternative embodiment offuel rail assembly 500. In this particular example, fuel rail assembly600 includes a plurality of fuel separation membrane elements 682, 684,and 686 forming respective regions 672, 674, and 676 for receiving thepermeant. Collectively regions 672, 674, and 676 can represent region135 shown in FIG. 1. While this example will be described as including aplurality of distinct membrane elements, it should be appreciated thatthese membrane elements can form a membrane element system, and can insome instances be supported within the fuel rail assembly by a commonsupport structure.

Fuel rail assembly 600 is shown including a fuel rail housing 610 havingat least one inlet port 620 for receiving a mixed fuel as indicated at642 and one or more fuel outlet ports, an example of which is shown at630. Fuel outlet port 630 can be fluidly coupled with a fuel injector632, for delivering fuel to at least one cylinder of the engine. Notethat fuel rail assembly 600 can include an outlet port for each cylinderserviced by the fuel rail assembly. Injector 632 can represent injector366 shown in FIG. 3.

A fuel mixture receiving region 670 within the fuel rail assembly is atleast partially defined by fuel rail housing 610. Region 670 canrepresent region 133 shown in FIG. 1. Fuel rail housing 610 in thisexample includes fuel rail wall 608 and end caps 650 and 652. Note thatwhile fuel rail assembly has been shown to include a fuel rail housinghaving end caps, in other examples, the end caps may integrally formedwith the fuel rail wall. In this way, the fuel rail housing can compriseone or more portions for purposes of manufacturing.

As shown in FIG. 6, fuel rail assembly 610 can include two or more fuelseparation membrane elements defining two or more independent fuelseparation regions. For example, fuel rail assembly 610 in this example,includes a first separation membrane element 682 defining a fuelseparation region 672, a second separation membrane element 684 defininga fuel separation region 674, and a third separation membrane element686 defining a fuel separation region 676. Thus, in this example, fuelrail assembly 610 includes three distinct fuel separation membraneelements. In some examples, these fuel separation membrane elements canbe supported and/or held in position within the fuel rail housing by oneor more supports indicated generally at 698. The supports may beprovided at prescribed intervals along the longitudinal length of themembrane elements. FIG. 7 shows an example cross section of support 698.

In this example, end cap 650 includes a plurality of openings fordispensing permeant from regions 672, 674, and 676 as shown respectivelyat 692, 694, and 696. These openings can each be fluidly coupled with acommon vapor passage, such as vapor passage 138 of FIG. 1.

FIG. 7A shows an example cross-section of fuel rail assembly 500,including fuel rail housing 510, fuel mixture region 570, fuelseparation membrane element 582, and fuel separation region 572. In thisexample, the fuel rail wall and fuel separation membrane element eachhave circular cross-sections. However, in other examples, the fuel railwall and/or fuel separation membrane element may have any suitablecross-section. FIG. 7B shows an example cross-section through support598 at a different location along the length of fuel rail assembly 500than the cross-section shown in FIG. 7A. FIG. 7B illustrates how support598 can be disposed between the membrane element and the fuel rail walland the membrane element, and may have various openings indicated at 570for permitting fuel to flow longitudinally along the length of the fuelrail. It should be appreciated that the shape of support 598 as shown inFIG. 7B is merely one example and that other suitable shapes may beused.

FIGS. 7C and 7D show other example cross sections for fuel rail assembly500. The inventors herein have recognized that by increasing the surfacearea of the fuel separation membrane element, the separation rate of thepermeant from the fuel mixture may be increased. Thus, the example ofFIGS. 7C and 7D show how the membrane element may include a plurality ofsides and/or folds that serve to increase the surface area of themembrane element relative to the internal volume of region 572 containedwithin the membrane element. FIG. 7D also shows an example cross-sectionthrough support 598 at a different location along the length of fuelrail assembly 500 than the cross-section shown in FIG. 7C. FIG. 7Dillustrates how support 598 can be disposed between the membrane elementand the fuel rail wall and the membrane element, and may have variousopenings indicated at 570 for permitting fuel to flow longitudinallyalong the length of the fuel rail.

FIG. 7E shows yet another example cross-section for fuel rail assembly600, which includes multiple independent permeant receiving regions,defined by separation membrane elements 682, 684, and 686. Note thatother fuel rail assemblies may include other suitable numbers of fuelseparation membrane elements to achieve a prescribed fuel separationrate. By increasing the quantity of fuel separation membrane elementsthat define distinct fuel separation regions, the total surface area ofthe membrane elements may be increased for a given volume of thepermeation region, thereby increasing the separation rate of thepermeant. Furthermore, by utilizing membrane element tubes having arelatively smaller cross-sectional area, circumference, or diameter, thering stress in the support structure of the membrane elements can bereduced, thereby allowing a reduction in wall thickness which canfurther increase permeation rate. Fuel rail wall 608 is shownsurrounding region 670. Membrane elements 682, 684, and 686 are shown ashaving a circular cross section defining regions 672, 674, and 676,respectively. Note that membrane elements 682, 684, and 686 can haveother suitable shapes. Furthermore, in some examples, at least one ormore of the membrane elements can have a different shape than anothermembrane element of the same fuel rail assembly. FIG. 7F shows anexample cross-section through support 698 at a different position alongthe longitudinal length of the fuel rail assembly than the cross-sectionof FIG. 7E. FIG. 7E illustrates how support 598 can be disposed betweenthe membrane element and the fuel rail wall and the membrane element,and may have various openings indicated at 670 for permitting fuel toflow longitudinally along the length of the fuel rail.

FIG. 8 shows a flow chart depicting an example routine for controllingthe relative amount of the first and the second fuels that are deliveredto the engine. At 810, operating conditions can be identified. As oneexample, control system 190 can identify operating conditions associatedwith the engine or engine system via one or more of the previouslydescribed sensors. Operating conditions may include one or more of thefollowing: engine speed, engine load, boost pressure, enginetemperature, ambient air temperature and pressure, exhaust temperature,intake or exhaust valve timing, throttle position, fuel mixture amountand composition stored on-board the vehicle, permeant amount and/orcomposition that has been separated from the fuel mixture, pressure offuel mixture within fuel rail assembly 130, pressure of permeant withinfuel rail 160, an indication of knock provided by a knock sensor,vehicle/engine operator input, exhaust catalyst conditions, and fuelpump conditions, among others.

At 820, the relative amounts of the first and second fuels to bedelivered to the engine can be selected in response to the operatingconditions identified at 810. As one example, control system 190 canreference a look-up table, map, or suitable fuel selection functionstored in memory. An example map is shown in FIG. 10 for selecting arelative amount of gasoline and ethanol to be delivered to the engine inresponse to various operating conditions. As one non-limiting example,where the permeant that is separated from the fuel mixture includes ahigher concentration of alcohol than the fuel mixture, then the amountof the permeant delivered to the engine relative to the retainedcomponents of the fuel mixture can be increased in order to reduceengine knock. Thus, the amount of the alcohol component that isdelivered to the engine can be increased relative to the amount of thehydrocarbon component in response to operating conditions that increasethe tendency for engine knock. These operating conditions may includeengine load, engine speed, and/or boost pressure, for example, amongothers.

At 830, the relative amounts of the first and second fuels that wereselected at 820 can be delivered to the engine at 830. For example, thecontrol system can control the fuel injectors to provide the prescribedrelative amounts of each fuel type to the various engine cylinders. Asshown in FIG. 3, injector 367 can inject the permeant and injector 366can inject the portion of the fuel mixture that was retained by themembrane element, where the permeant can include a greater concentrationof alcohol than the fuel injected by injector 366. In some examples, thecontrol system can utilize feedback control from an exhaust gas sensorto adjust the relative amounts of the two fuels actually delivered tothe engine based on the relative amounts prescribed by the controlsystem.

At 840, it can be judged whether there is an indication of knock. As oneexample, the control system can receive an indication of engine knockfrom a knock indicating sensor shown at 396 in FIG. 3. If the answer at840 is yes, the amount of a knock suppressing fuel (e.g. the alcoholcomponent) delivered to the engine can be increased relative to theother fuel type (e.g. the hydrocarbon component) at 850. For example,the control system can increase the amount of the permeant that isdelivered to the engine (e.g. via injector 367 as indicated at 180)relative to the amount of the remaining fuel mixture retained by themembrane element (e.g. via injector 366 as indicated at 170) in order toreduce engine knock.

Note that the amounts of the first and second fuels delivered to theengine via 170 and 180, for example, may be adjusted based on variousoperating conditions, such as engine operating conditions as notedabove, separation performance, ambient conditions, etc. In one example,the amounts of the first and second fuels may be adjusted responsive toexhaust air-fuel ratio. Further, the selection of whether to adjust thefirst and/or second fuel based on exhaust air-fuel ratio may be informedby performance of the separation, such as based on fuel rail pressureand/or fuel rail temperature. In this way, improved air-fuel control maybe obtained.

Referring now to FIG. 9, a flow chart is shown depicting an examplecontrol routine for controlling the separation rate of at least one fuelcomponent from a fuel mixture via membrane element containing fuel railassemblies described herein. At 910, operating condition can beidentified as previously described at 810.

At 912, it may be judged whether to increase the separation rate of thefuel mixture. As one non-limiting example, the control system may decideto increase the separation rate of the fuel mixture to obtain anincreased supply rate of the alcohol rich permeant. The control systemcan receive feedback as to the amount and/or concentration of theseparated permeant fuel that is available to the engine via sensors 153and 155. The control system can also consider the current and/orpredicted usage rates of the permeant based on the identified operatingconditions. For example, where the engine is operated by the vehicleoperator such that the alcohol rich permeant fuel is supplied to theengine at a relatively higher rate in order to reduce knock tendency,the control system can correspondingly increase the separation rate ofthe fuel mixture so that a sufficient quantity of the alcohol richcomponent is available for delivery to the engine. As one example, thecontrol system may reference a look-up table, map, or function stored inmemory to determine an appropriate separation rate based on the usagerate of the fuel as judged from the operating conditions identified at810 or 910.

If the answer at 912 is yes, the routine can proceed to 914. At 914, thepressure of the fuel mixture supplied to the fuel rail assembly may beincreased by the control system by increasing the amount of pump workprovided by pumps 122 and/or 126. For example, the control system canincrease the speed of the motor driving pump 122 and/or increase theeffective volume of each pump stroke of pump 126. Additionally, thecontrol system can adjust the pulse width of the fuel injectorsassociated with the fuel rail assembly (e.g. injector 366) to maintainthe prescribed injection amount identified using the routine of FIG. 8,even in response to the pressure increase. For example, where the fuelpressure of the fuel rail assembly is increased, namely the fuelpressure within region 133 of the fuel rail assembly, the pulse width ofthe fuel injectors may be reduced to correspond to the prescribedinjection amount.

At 916, the concentration of the permeant vapor within region 135 of thefuel rail assembly can be reduced by increasing the removal rate fromthe fuel rail assembly vapor passage 138. In other words, the controlsystem can increase the concentration gradient of the alcohol componentacross the membrane element in order to increase the rate of permeationand hence increasing the rate of separation.

At 918, the temperature of the fuel rail assembly can be adjusted toincrease the separation rate of the permeant from the fuel mixture. Forexample, the control system can increase or decrease the amount of heatproduced by the engine, the engine coolant flow rate, and/or othersuitable cooling parameters in order to increase the separation rateprovided by the fuel rail assembly.

Alternatively, if the answer at 912 is no, the routine can proceed to920. At 920 it can be judged whether to reduce the separation rate ofthe fuel mixture. The considerations used by the control system for thedecision at 912 can be similar to those applied at the decision at 920.For example, if the engine is operated such that the use of permeant isreduced or discontinued and the permeant storage tank has a sufficientamount of permeant, then the control system may reduce the separationrate. If the answer at 920 is yes, the routine can proceed to 922.Alternatively, if the answer at 922 is no, the routine can return.

At 922, the pressure of the fuel mixture supplied to the fuel railassembly can be reduced by the control system by adjusting pumps 122and/or 126. Additionally, the pulse width of the fuel injectorsassociated with the fuel rail assembly (e.g. injector 366) can beincreased in response to the pressure reduction to maintain the sameeffective fuel delivery amount.

At 924, the concentration of the permeant vapor within region 135 can beincreased by reducing the removal rate and/or condensation rate of thepermeant vapor from region 135. In other words, the control system canadjust the condenser pump and/or the heat exchanger to reduce theconcentration gradient across the membrane element, thereby reducing theseparation rate of the fuel mixture. At 926, the temperature of the fuelrail assembly can be adjusted in an appropriate direction to reduce theseparation rate of the fuel mixture. From either of 918 and 926, theroutine can return.

FIG. 10 shows a graph or map depicting an example strategy forcontrolling the relative amounts of an alcohol rich fuel such as ethanoland a hydrocarbon rich fuel such as gasoline that are delivered to theengine for a range of operating conditions affecting engine knock. Thehorizontal axis of the graph represents knock tendency or the level ofknock suppression necessary to reduce or eliminate engine knock. Thevertical axis of the graph represents the amount of ethanol delivered tothe engine relative to gasoline. When the knock tendency is relativelylow, the amount of ethanol delivered to the engine relative to gasolinecan be reduced or minimized. For example, where there is low knocktendency, only injector 366 may be operated to deliver the fuel mixturethat has been retained by the membrane element to the cylinder. As theknock tendency is increased by increasing the engine speed, engine load,and/or boost pressure provided by a boosting device, the amount ofethanol provided to the engine can be increased relative to the amountof gasoline by increasing the amount of the permeant that is injectedvia injector 367. As indicated at 1020, this increase in permeantinjection may include an amount that corresponds to a minimum pulsewidth of the injector (e.g. injector 367). As indicated at 1010, theamount of ethanol delivered to the engine may be increased relative tothe amount of gasoline as the engine speed, engine load, and/or boostpressure continues to increase. For example, the control system canincrease the amount of the permeant delivered to the engine relative tothe amount of the fuel mixture that was retained by the membraneelement. In this way, the control system can control the relativeamounts of the different fuels, previously derived from a common fuelmixture, that are delivered to the engine in response to operatingconditions to reduce engine knock.

1. A method of operating an engine fuel system, comprising: supplying apressurized fuel mixture to a first fuel rail, said fuel mixtureincluding a hydrocarbon component and an alcohol component; separatingat least a portion of the alcohol component from the fuel mixture bypassing at least said portion of the alcohol component through a fuelseparation membrane element disposed within the first fuel rail toobtain an alcohol reduced fuel mixture, the membrane element beingpermeable and comprising a polymer; delivering the alcohol reduced fuelmixture from the first fuel rail to at least a cylinder of the enginevia a first fuel injector fluidly coupled with the first fuel rail;supplying the separated alcohol component from the first fuel rail to asecond fuel rail; and delivering the separated alcohol component fromthe second fuel rail to the cylinder via a second fuel injector fluidlycoupled with the second fuel rail.
 2. The method of claim 1, wherein thesecond fuel injector is configured as a direct in-cylinder fuel injectorand wherein said delivering the alcohol fuel component to the cylinderincludes directly injecting the alcohol fuel component into the cylindervia the second fuel injector.
 3. The method of claim 2, wherein thefirst fuel injector is configured as a direct in-cylinder fuel injectorand wherein said delivering the alcohol reduced fuel mixture to thecylinder includes directly injecting the alcohol reduced fuel mixtureinto the cylinder via the first fuel injector.
 4. The method of claim 3,wherein said supplying a pressurized fuel mixture to the first fuel railis performed via at least a first lower pressure fuel pump that ispowered by an electric motor and a second higher pressure fuel pump thatis powered by a mechanical output of the engine.
 5. The method of claim1, wherein said supplying a pressurized fuel mixture to the first fuelrail is performed via at least a first fuel pump; and wherein saidsupplying the separated alcohol component from the first fuel rail tothe second fuel rail further comprises increasing pressurization of theseparated alcohol component via a second fuel pump.
 6. The method ofclaim 1, wherein said supplying the separated alcohol component from thefirst fuel rail to the second fuel rail further comprises condensing avapor phase portion of the separated alcohol component to a liquid phaseat a condensation tank before the separated alcohol component issupplied to the second fuel rail in the liquid phase.
 7. The method ofclaim 1, further comprising: increasing intake air pressure supplied tothe cylinder by boosting said intake air via a compression device; andincreasing an amount of the alcohol component delivered to the cylinderrelative to the hydrocarbon component in response to an increase of theintake air pressure supplied to the cylinder via the compression device.8. The method of claim 1, further comprising, heating the first fuelrail with heat generated by the engine, and where the alcohol reducedcomponent is delivered to a plurality of cylinders.
 9. A method for anengine fuel system, comprising: supplying a fuel mixture to a rail, saidfuel mixture including a hydrocarbon component and an alcohol component;separating at least a portion of the alcohol component from the fuelmixture by passing at least said portion of the alcohol componentthrough a fuel separation membrane element disposed within the rail toobtain an alcohol reduced fuel mixture, the membrane element beingpermeable and comprising a polymer; delivering the alcohol reduced fuelmixture from the rail to at least a plurality of cylinders of the enginevia injectors; and supplying the separated alcohol component to theplurality of cylinders.
 10. The method of claim 9 where the separatedalcohol component is delivered in a vapor phase to the engine.
 11. Themethod of claim 9 where the separated alcohol component is delivered ina pressurized liquid phase to the engine.
 12. The method of claim 9where the injectors are coupled directly to the rail.
 13. The method ofclaim 9 further comprising pressurizing the fuel mixture with a highpressure fuel pump.
 14. The method of claim 9 where a pressure of thepressurized fuel mixture is adjusted responsive to an exhaust gas oxygenamount.
 15. A method of operating a fuel system for an internalcombustion engine, comprising: supplying a pressurized fuel mixture to afuel rail, said fuel mixture including a hydrocarbon component and analcohol component; separating at least a portion of the alcoholcomponent from the fuel mixture by passing at least said portion of thealcohol component through a fuel separation membrane element disposedwithin the fuel rail to obtain an alcohol reduced fuel mixture, themembrane element being permeable and comprising a polymer; delivering atleast a portion of the alcohol reduced fuel mixture from the fuel railto at least a plurality of cylinders of the engine via injectors fluidlycoupled with the first fuel rail; supplying at least a portion of theseparated alcohol component to the engine; and adjusting at least one ofthe delivery of the alcohol reduced fuel mixture and the supply of theseparated alcohol component responsive to variation in engine operatingconditions.
 16. The method of claim 15 further comprising adjusting thedelivery of the alcohol reduced fuel mixture responsive to exhaustair-fuel ratio.
 17. The method of claim 15 further comprising adjustingsupply of the separated alcohol component responsive to exhaust air-fuelratio.
 18. The method of claim 15 further comprising at least partiallycondensing the portion of separated alcohol component before supplyingit to the engine, where the condensing is adjusted responsive to anoperating condition.